Illinois
Fertilizer Conference Proceedings
January 27-29, 1992
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F.E. Below, P.S. Brandau, and D.G. Bullock1
As public awareness focuses on environmental quality, there are increasing pressures for growers and fertilizer dealers to justify the levels of N fertilizer they are recommending or using. The overall goal of this research is to determine if soil and/or tissue tests can be used to optimize N management practices for corn production in Illinois.
Plants of two genetically distinct corn hybrids (B73xLH51 and LHE136xLH82) were grown with varying rates of applied nitrogen (from 0 to 250 lbs N per acre) at four diverse sites in 1990 and 1991. The sites (one in Champaign and Tremont, and two in Geneseo) were selected to represent a range in inherent soil fertility and cultural practices. At several stages during plant growth, soil was sampled from unfertilized plots (which contained plants) and analyzed for NO3-N and NH4-N. Although numerous dry matter and N use parameters were measured, only grain yield and soil N levels are presented in this report. Grain yield of both hybrids was significantly increased from applications of fertilizer N at three of the four locations in 1990, and at two of the locations in 1991. For N responsive sites, maximum yield usually occurred at an N rate of approximately 200 lbs per acre. At these sites, plants grown without fertilizer N produced from 66 to 82% of the maximum yield. The site which was nonresponsive to fertilizer N (Geneseo 1), has regularly received swine manure and has a high level of residual soil N. Soil analysis before planting and at the six inch corn ,stage gave comparable total N values, but the predominant N form (i.e. NO3-N or NH4-N) often changed. This change in N form, and the high percentage of N as NH4-N at the Geneseo 1 site, limited the usefulness of soil NO3-N levels in predicting responsiveness to fertilizer N. Regardless of N rate, the hybrid B73xLH51 outyielded LHE136x LH51 at these same locations in 1991.
These preliminary findings show the variable effect of management practices,
hybrid selection, and environment on yield response of corn to fertilizer N.
Although these data suggest an opportunity to improve fertilizer N management
in Illinois, they also demonstrate the importance of annual applications of
an N source to obtain maximum corn productivity.
Nitrogen fertilizer is routinely used by Illinois corn growers because soils do not have sufficient N in available form to support desired production levels. However, each year growers face the dilemma of knowing how much N fertilizer is required. This problem is further complicated by limitations associated with convenience of fertilizer N application, and by uncertainty related to weather conditions, especially water availability. For these reasons, it is understandable why some producers may misapply (either too much or too little) the N rate needed for optimum productivity.
Although countless studies have examined corn yield response to N fertilization, widespread recommendations are difficult due to the complex cycle of N in the environment. Currently, N fertilizer recommendations in Illinois are based on expected yield goal and formulas estimating the residual soil supply (based on soil type and organic matter, previous crop, and the amount of manure applied). Although generally sound, problems can arise with this approach if the expected yield goal is unrealistic or if growers fail to accurately assess the residual soil N supply. Recent research indicating that yield response to,fertilizer N is also influenced by form of N, timing of application, and genotype grown further complicates N management recommendations.
The tendency to over, or under, fertilize could be reduced if corn growers had a quick and reliable method to assess availability of residual soil N, with adequate time to correct deficiencies. In this regard, two new technologies being evaluated for predicting fertilizer N requirements include the Late Spring Soil Nitrate Test and the handheld leaf chlorophyll meter. These technologies have an advantage' over leaf tissue tests in that they can also be used as a tool to improve N fertilizer management., For example, soils with nitrate levels less than 21 parts-per-million are much more likely to respond to fertilizer applied N than are those with nitrate levels greater than 21 parts-permillion (Blackmer et al., 1989; McCracken et al., 1989; and our unpublished data). Similarly, leaf chlorophyll nneasurements with the SPAD 502 meter provides a way to rapidly assess leaf N status as there is a close relationship between leaf N concentrations and leaf greenness (Schepers et al., 1990; Schepers et al. 1991). Although additional testing is needed, these new techniques offer promise for predicting N fertilizer needs and improving production efficiency.
Thus, the objective of this research is to determine if soil and/or tissue
samples can be used to optimize N management practices for corn production in
Illinois. Specifically, this work is attempting to relate levels of residual
soil N with the anticipated yield response to applications of fertilizer N.
Tissue samples from plants grown with varying rates of fertilizer N are being
used in conjunction with soil samples to determine the plant's ability to utilize
residual and fertilizer applied N. It is hoped that this research will lead
to ways of using soil and tissue analyses to ensure adequate levels of N are
available to optimize production efficiency and safeguard environmental quality.
Two genetically distinct corn hybrids (B73xLH51 and LHE136xLH82) were evaluated for response to fertilizer applied N at four diverse locations in Illinois in 1990 and 1991. The individual locations and some of their soil characteristics are presented in Table 2. Briefly, the locations include: 1) the Agronomy-Plant Pathology South Farm at the University of Illinois, Champaign which is devoted to agricultural research and has irrigation capabilities; 2) a grain farm in Tremont (near Peoria) which is part of a high-management corn/soybean rotation; 3) a livestock/grain operation in Geneseo (Geneseo 1) that received known amounts of hog manure and is in continuous corn; and 4) a separate site in Geneseo (Geneseo 2), that is part of a corn/soybean rotation and does not receive manure.
Treatments consisted of each hybrid grown with varying levels of soil applied N. At all locations, the experiment was arranged in a split-plot design with three to four replications. At Champaign, N rates were main plots and hybrids the subplots, while at the other three locations hybrids were the main plots and N rates the subplots. An experimental unit consisted of eight rows of the respective hybrid that- were either 20 feet (Champaign and Tremont) or 40 feet (both Geneseo locations) in length. At Tremont, rows were spaced 36 inch apart, while the row spacing was 30 inches at the other locations. At all locations, the stand density was 26,000 plants per acre. In 1990, the N levels tested were 0, 60, 120, 180, and 2401bs N per acre at Champaign; 0, 50, 150, and 200 lbs N per acre at Tremont, and 0, 25, 50, 75, 100, 125, 150, 175, and 2001bs N per acre at both Geneseo locations. The same levels were used at each location in 1991 except for addition of a 250 lb N rate at Tremont and 2251b rates at both of the Geneseo locations. The N treatments were established when plants were at the V2 to V3 growth stage by applying varying amounts of urea or ammonium nitrate and immediately incorporating with cultivation. Six of the eight rows received the fertilizer treatment and the two outside rows served as borders.
Prior to planting, the soil at each site was sampled (to a depth of 12 inches) for analysis of available NO3 and NH4. Other samples were taken from plots that did not receive fertilizer N but that contained six inch plants. At flowering and physiological maturity, the above ground portions of four representative plants were harvested from each plot, separated into leaves, stalk (including leaf sheaths), grain, and a reproductive support fraction consisting of husk, shank, tassel and cob. After drying (80°C) to constant weight, all fractions were weighed, ground, and analyzed for total N. Although not included in this report, these data are being used to determine the effect of N rate on: 1) accumulation and partitioning of total N and dry matter by the plant; 2) the amount of these constituents accumulated after flowering, and 3) the proportion of grain N derived from remobilization.
Once the grain had field-dried to an acceptable moisture content, the center
two rows of each plot were combine harvested for the two Geneseo locations and
hand harvested for the other two locations in order to estimate grain yield.
Yield is expressed as bushels per acre at 15.5 % moisture.
Grain yields of both hybrids were significantly increased from applications of fertilizer N at three of the four locations in 1990 and at two locations in 1991 (Fig 1). These included Champaign and Tremont in both years and one of the Geneseo locations (Geneseo 2) in 1990. For each of these N responsive sites, maximum yields were obtained with- an N rate of approximately 200 lbs per acre. Plants relying solely on soil residual N produced from 66 to 82% of the maximum yield. With the exception of Tremont, grain yields and/or the response to applied N was greater in 1990 than in 1991.
As expected, the response to fertilizer applied N exhibited a pattern of decreasing increments of yield increase with successive N rates (Fig 1). Because yields had not plateaued at the Tremont or Geneseo 2 sites in 1990, it is unclear if additional N would have resulted in even higher yields. However, increasing the high N rate by 25 lbs at Geneseo 2 and 50 lbs at Tremont did not result in higher yields in 1991. In contrast, yields did plateau at the responsive Champaign site, with a hint of a yield decrease at the highest N rate (240 lbs) in 1991. The Geneseo 1 site, which was nonresponsive to fertilizer N in both years, has regularly received large amounts of swine manure and has a high level of residual soil N (table 2).
Soil analysis revealed differences among the locations in the level of residual soil N, as well as differences in the predominant form of N (Table 2). Comparison of soil N levels prior to planting with those at the six inch corn stage showed little change in total inorganic N levels at any of the locations in either year. However, at some locations, the predominant N form changed between sampling dates. For example, at Tremont in 1991, the majority (67%) of residual soil N was present as NH4-N prior to planting, while NO3-N was the principle form (72 %) at the six inch stage (Table 2). Although the Geneseo 1 location always had the highest level of total soil N, a large and variable, proportion of this N (32 to 70%) was present as NH4-N. As a result, soil NO3-N levels were often below the threshold for N sufficiency, indicating a need for additional fertilizer N. Lack of yield response to N at this site (Fig 1) indicates an important limitation of the soil nitrate test when NH4-N constitutes a large proportion of the residual soil N.
Other wrong predictions of N requirement based on soil NO3-N levels are also apparent in this data, which are not related to the level of soil NH4-N. Specifically, low soil NO3-N levels at Geneseo 2 in 1991 indicated the need for additional N, yet yield at this site did not respond to N fertilizer. Although this data demonstrates problems associated with the soil NO3-N test, it shows that responsiveness to N fertilization may be related to total inorganic soil N (i.e. NO3-N + NH4-N). For example, the lack of response at Geneseo 1 in 1990, and at both Geneseo location in 1991, might have been indicated by total residual soil N levels that were at or greater than 30 parts-permillion (Table 2).
Regardless of N rate, the hybrid B73xLH5l outyielded LHE136xLH82 at three locations in 1990 (Champaign, Geneseo 1 and 2) while LHE136xLH82 outyielded B73xLH51 at these same locations in 1991. Although the reason for this difference in unclear, these hybrids were selected for study based on differences in their utilization of N. In this regard, LHE136xLH82, which is generally less responsive to N, did better in the lower yielding environment of 1991, while the N responsive hybrid B73xLH51 performed best in the high yielding environment of 1990. Collectively, these data demonstrate the variable effect of management practices, hybrid selection, and environment on yield responsiveness of corn to fertilizer applied N.\
As public awareness focuses on environmental quality there are increasing pressures for corn growers and fertilizer dealers to justify the levels of N fertilizer they are recommending or using. This concern is prompted by the discovery of nitrates in ground water and a public perception that growers over-apply fertilizer N. The research being conducted in this project is prompted by these concerns. Reliable and up to date information on how corn plants use N will add to information required to improve N management of Illinois soils, and will help to minimize the adverse environmental impacts of N fertilizer use.
In addition to helping address the question of how much fertilizer N is needed to optimize production efficiency, this research is also examining N use and fertilizer needs from a plant perspective. Information regarding the physiological basis for requirement and use of N with current hybrids and management strategies is surprisingly lacking. The findings obtained so far indicate several instances when soil nitrate levels do not accurately predict the responsiveness to N fertilizer. This problem occurs because management practices, hybrid selection, and environment all interact to determine the need for fertilizer N. However, despite limitations of the soil nitrate test, we still believe that N management could be improved by the ability to better predict the plant's need for fertilizer N. Thus additional research is needed to relate soil N availability with plant use and productivity.
1F.E. Below is Associate Prof. of Plant Physiology, P.S. Brandau is Research Specialist in Agriculture and D.G. Bullock is Assistant Professor of Crop Production, all in the Department of Agronomy, University of IL at Urbana-Champaign. This study was supported in part by a grant from the Fertilizer Education and Research Council.
Blackmer, A.M., D. Pottker, M.E. Cerato, and J. Webb. 1989. Correlations between
soil nitrate concentration in late spring and corn yields in Iowa. J. Prod.
Agric. 2:103-109.
McCracken, D.V., S.J. Corak, M.S. Smith, W.W. Frye, and R.L. Blevins. 1989.
Residual, effects of nitrogen fertilization and winter cover cropping on nitrogen
availability. Soil Sci. Soc. Am. J. 53:1459-1464.
Schepers, J.S., D.D. Francis, and C. Clausen. 1990. Techniques to evaluate
N status of corn. p. 280. In Agronomy Abstracts. ASA, Madison, WI.
Schepers, J.S., D.D. Frances, J.F. Vigil, and T. Blackmer. 1991. Use of chlorophyll
meters to evaluate N status of corn. p. 300. In Agronomy Abstracts. ASA, Madison,
WI.
